The effect of copper concentration on the performance of the catalytic reaction between silicon and methyl chloride was investigated using online gas chromatogram. The catalyst concentration greatly influences various...The effect of copper concentration on the performance of the catalytic reaction between silicon and methyl chloride was investigated using online gas chromatogram. The catalyst concentration greatly influences various aspects of the direct organosilane synthesis process, including the reaction rate, the selec- tivity, and the silicon conversion. The reaction activity and the silicon conversion increase as the catalyst concentration increases. However, the reaction selectivity decreases for the catalyst concentrations more .than 9 wt.%. The cross-sections of deactivated contact mass particles were observed by optical microscopy and analyzed by scanning electron microscope combined with energy dispersive X-ray detector （SEM-EDX） The observations showed that a textured substance formed on the original flat surface of the silicon particles after deactivation with copper only in a shallow surface layer of the contact mass. This indicates that the copper diffusion is the rate limiting step which causes the reaction deactivation.展开更多
A one-dimensional unsteady mathematical model was established to describe direct reduction in a composite pellet made of metallurgical dust. The model considered heat transfer, mass transfer, and chemical reactions in...A one-dimensional unsteady mathematical model was established to describe direct reduction in a composite pellet made of metallurgical dust. The model considered heat transfer, mass transfer, and chemical reactions including iron oxide reductions, zinc oxide reduction and carbon gasification, and it was numerically solved by the tridiagonal matrix algorithm （TDMA）. In order to verify the model, an experiment was performed, in which the profiles of temperature and zinc removal rate were measured during the reduction process. Results calculated by the mathematical model were in fairly good agreement with experimental data. Finally, the effects of furnace temperature, pellet size, and carbon content were investigated by model calculations. It is found that the pellet temperature curve can be divided into four parts according to heating rate. Also, the zinc removal rate increases with the increase of furnace temperature and the decrease of pellet size, and carbon content in the pellet has little influence on the zinc removal rate.展开更多
With a weak hyperon-hyperon （YY） interaction deduced from the new experimental data of AA potential, this paper has performed a calculation of the direct Urca （DURCA） processes in the framework of the relativistic...With a weak hyperon-hyperon （YY） interaction deduced from the new experimental data of AA potential, this paper has performed a calculation of the direct Urca （DURCA） processes in the framework of the relativistic mean field theory （RMFT） including σ＊ and φ mesons, in comparison with the results calculated with the strong YY interaction and with no （σ＊ ,φ ） mesons included. In neutron star matter, the weak YY interaction supplies the additional repulsive interaction between hyperons while the strong YY interaction supplies the attractive one. With the weak YY interaction, the effective masses of hyperons are larger than those with the strong YY interaction while smaller than those with no （σ＊ ,φ） mesons included. The threshold star masses for the DURCA processes involving nucleons and A are not sensitive to the strength of the YY interaction. The weak YY interaction leads to larger threshold masses for the DURCA process involving [1]1 and [1]0 than the other two cases. The process involving [1]0 can take place in the neutron star only when the weak YY interaction is used. The weak YY interaction is able to bring in the agreement with the observation of the neutron star with larger mass and faster cooling than the strong YY interaction.展开更多
In the framework of the relativistic mean field theory （RMFT）, the relativistic energy losses of the direct Urea processes with hyperons （Y-DURCA ） for reactions A → p ＋ e ＋ υe and ≡^-→ A＋e＋υe are studied...In the framework of the relativistic mean field theory （RMFT）, the relativistic energy losses of the direct Urea processes with hyperons （Y-DURCA ） for reactions A → p ＋ e ＋ υe and ≡^-→ A＋e＋υe are studied in neutron stars. We calculate the energy gap of A hyperons and investigate the effects of the ^1S0 superfluidity （SF） of A hyperons on the Y-DURCA processes. The calculated results are in line with the recent experimental data △ BAA ～ 1.01 ±0.20-0.11^＋0.18 MeV. The results indicate that the ^1S0 SF of A hyperons exists in most density ranges of happening the two reactions. The theoretical cooling curves are in agreement with observation data.展开更多
In non-homogeneous environment, traditional space-time adaptive processing doesn＇t effectively suppress interference and detect target, because the secondary data don＇ t exactly reflect the statistical characteristi...In non-homogeneous environment, traditional space-time adaptive processing doesn＇t effectively suppress interference and detect target, because the secondary data don＇ t exactly reflect the statistical characteristic of the range cell under test. A ravel methodology utilizing the direct data domain approach to space-time adaptive processing （ STAP ） in airbome radar non-homogeneous environments is presented. The deterministic least squares adaptive signal processing technique operates on a ＂snapshot-by-snapshot＂ basis to dethrone the adaptive adaptive weights for nulling interferences and estimating signal of interest （SOI）. Furthermore, this approach eliminates the requirement for estimating the covariance through the data of neighboring range cell, which eliminates calculating the inverse of covariance, and can be implemented to operate in real-time. Simulation results illustrate the efficiency of interference suppression in non-homogeneous environment.展开更多
The resonant excitation is used to generate photo-excited carriers in quantum wells to observe the process of the carriers transportation by comparing the photoluminescence results between quantum wells with and witho...The resonant excitation is used to generate photo-excited carriers in quantum wells to observe the process of the carriers transportation by comparing the photoluminescence results between quantum wells with and without a p-n junction. It is observed directly in experiment that most of the photo-excited carriers in quantum wells with a p-n junction escape from quantum wells and form photoeurrent rather than relax to the ground state of the quantum wells. The photo absorption coei^cient of multiple quantum wells is also enhanced by a p-n junction. The results pave a novel way for solar cells and photodetectors making use of low-dimensional structure.展开更多
The relativistic neutrino emissivity of the nucleonic direct URCA processes in neutron star matter is investigated within the relativistic Hartree-Fock approximation. We particularly study the influences of the tensor...The relativistic neutrino emissivity of the nucleonic direct URCA processes in neutron star matter is investigated within the relativistic Hartree-Fock approximation. We particularly study the influences of the tensor couplings of vector mesons ω and ρ on the nucleonic direct URCA processes. It is found that the inclusion of the tensor couplings of vector mesons w and p can slightly increase the maximum mass of neutron stars. In addition, the results indicate that the tensor couplings of vector mesons ω and ρ lead to obvious enhancement of the total neutrino emissivity for the nucleonic direct URCA processes, which must accelerate the cooling rate of the non- superfluid neutron star matter. However, when considering only the tensor coupling of vector meson ρ, the neutrino emissivity for the nucleonic direct URCA processes slightly declines at low densities and significantly increases at high densities. That is, the tensor coupling of vector meson ρ leads to the slow cooling rate of a low-mass neutron star and rapid cooling rate of a massive neutron star.展开更多
In this study,innovative ellipsoid pellet with craters on its surface was designed,and the direct reduction process was compared with ellipsoid(without craters)and sphere pellets.In addition,furnace temperature and un...In this study,innovative ellipsoid pellet with craters on its surface was designed,and the direct reduction process was compared with ellipsoid(without craters)and sphere pellets.In addition,furnace temperature and uneven heat flux density effects on the pellet direct reduction process were also studied.The results show that ellipsoid pellet is better than that of spherical pellet on metallization ratio.However,under the condition of non-uniform heat flow,the ellipsoid pellet final metallization rate and zinc removal rate were lower.Although the heat transfer effect of ellipsoid pellet with craters was not improved significantly,the metallization rate and zinc removal rate were found improved,which will have a cumulative effect on the pellets direct reduction process in rotary hearth furnace.Under varying furnace temperature conditions,the pellet temperature was higher than that of the constant furnace temperature.After 1200 s,pellet Fe concentration increased to 123.6%,metallization rate and zinc removal rate increased to 113.7%and 102.2%,respectively.These results can provide references for the carbon-containing pellet design used in rotary hearth furnace.展开更多
Currently, the majority of copper tailings are not effectively developed. Worldwide, large amounts of copper tailings generated from copper production are continuously dumped, posing a potential environmental threat. ...Currently, the majority of copper tailings are not effectively developed. Worldwide, large amounts of copper tailings generated from copper production are continuously dumped, posing a potential environmental threat. Herein, the recovery of iron from copper tailings via low-temperature direct reduction and magnetic separation was conducted; process optimization was carried out, and the corresponding mineralogy was investigated. The reduction time, reduction temperature, reducing agent (coal), calcium chloride additive, grinding time, and magnetic field intensity were examined for process optimization. Mineralogical analyses of the sample, reduced pellets, and magnetic concentrate under various conditions were performed by X-ray diffraction, optical microscopy, and scanning electron microscopy-energy-dispersive X-ray spectrometry to elucidate the iron reduction and growth mechanisms. The results indicated that the optimum parameters of iron recovery include a reduction temperature of 1150A degrees C, a reduction time of 120 min, a coal dosage of 25%, a calcium chloride dosage of 2.5%, a magnetic field intensity of 100 mT, and a grinding time of 1 min. Under these conditions, the iron grade in the magnetic concentrate was greater than 90%, with an iron recovery ratio greater than 95%.展开更多
The solute redistribution in directional melting process is theoretically studied. Based on quantitative evaluations, uniform.solute distribution in liquid and a quasi-steady solute distribution in solid are supposed....The solute redistribution in directional melting process is theoretically studied. Based on quantitative evaluations, uniform.solute distribution in liquid and a quasi-steady solute distribution in solid are supposed. The discussion on the solute balance comes to a simple model for the solute redistribution in directional melting process. As an example, the variation of liquid composition during melting process of carbon steel is quantitatively evaluated using the model. Results show that the melting of an alloy starts at solidus temperature, but approaches the liquidus temperature after a very short transient process.展开更多
The microstructures and mechanical properties of a series of direct-quenched steels containing,in weight percent,from 0.05 to 0.20 carbon,0.20 to 0.40 silicon,1.10 to 1.70 manganese and at least one microalloying elem...The microstructures and mechanical properties of a series of direct-quenched steels containing,in weight percent,from 0.05 to 0.20 carbon,0.20 to 0.40 silicon,1.10 to 1.70 manganese and at least one microalloying element of vanadium,niobium,titanium and boron have been investigated.After controlled rolling,these steels were cooled in spray water to 400,300 and 200℃,respectively and then cooled in still air.Comparison of the Charpy V-notch impact toughness of direct-quenched steels without subsequent tempering was made with that of direct-quenched steels tempered at 600℃.It is found that an attractive combination of strength and toughness is achived by means of direct-quenching.There exists two types of microstructures in accordance with carbon equivalent.Lath martensitic microstructure is obtained for C>0.4%,granular bainitic microstructures for C.< 0.35%and mixtures of martensite and bainite for C,.in the range of 0.35— 0.40%.The effect of interrupted quenching temperature on microstructure is not significant for low C.steel,but interrupted quenching temperature has a strong effect on microstructure for high C,.steel.展开更多
A novel universal preprocessing method is proposed to estimate angles of arrival,which is applicable to one-or two-dimensional high resolution processing based on arbitrarycenter-symmetric arrays (such as uniform line...A novel universal preprocessing method is proposed to estimate angles of arrival,which is applicable to one-or two-dimensional high resolution processing based on arbitrarycenter-symmetric arrays (such as uniform linear arrays, equal-spaced rectangular planar arraysand symmetric circular arrays). By mapping the complex signal space into the real one, the newmethod can effectively reduce the computation needed by the signal subspace direction findingtechniques without any performance degradation. In addition, the new preprocessing scheme itselfcan decorrelate the coherent signals received on the array. For regular array geometry such asuniform linear arrays and equal-spaced rectangular planar arrays, the popular spatial smoothingpreprocessing technique can be combined with the novel approach to improve the decorrelatingability. Simulation results confirm the above conclusions.展开更多
In several stress responsive gene loci of monocot cereal crops,we have previously identified an unusual posttranscriptional processing mediated by paired presence of short direct repeated （SDR） sequences at 5＇ and ...In several stress responsive gene loci of monocot cereal crops,we have previously identified an unusual posttranscriptional processing mediated by paired presence of short direct repeated （SDR） sequences at 5＇ and 3＇ splicing junctions that are distinct from conventional （U2/U12-type） splicing boundaries.By using the known SDR-containing sequences as probes,24 plant candidate genes involved in diverse functional pathways from both monocots and dicots that potentially possess SDR-mediated posttranscriptional processing were predicted in the GenBank database.The SDRs-mediated posttranscriptional processing events including cis-and trans-actions were experimentally detected in majority of the predicted candidates.Extensive sequence analysis demonstrates several types of SDR-associated splicing peculiarities including partial exon deletion,exon fragment repetition,exon fragment scrambling and trans-splicing that result in either loss of partial exon or unusual exonic sequence rearrangements within or between RNA molecules.In addition,we show that the paired presence of SDR is necessary but not sufficient in SDR-mediated splicing in transient expression and stable transformation systems.We also show prokaryote is incapable of SDR-mediated premRNA splicing.展开更多
Objective: To characterise a novel multifunctional pharmaceutical excipient and investigate its ef ect on paracetamol release from tablets prepared by direct compression.Methods: The excipient was prepared by co-proce...Objective: To characterise a novel multifunctional pharmaceutical excipient and investigate its ef ect on paracetamol release from tablets prepared by direct compression.Methods: The excipient was prepared by co-processing gelatinized maize starch with sodium carboxymethyl cellulose and microcrystalline cellulose in a ratio of 2:1:1, dried and pulverized into powder. The excipient formulated was characterized using Fourier transform infrared spectroscopy and dif erential scanning calorimetry. The excipient was used to prepare batches of tablets by direct compression with drug-excipient ratios of 1:1, 1:2, 1:3 and 1:4. Parameters evaluated on tablets include crushing strength, friability and in vitro dissolution studies. Results: Differential scanning calorimetry analysis revealed a crystalline excipient while Fourier transform infrared spectroscopy showed no interaction between the excipient and paracetamol. Tablets from all the batches gave average crushing strength values between 3.47 and 4.88 kp. The 1:1 and 1:2 tablet batches were comparable to each other while 1:3 and 1:4 were also comparable to one another in their dissolution proi les. The dissolution parameters of the 1:4 batch was faster with- m∞(90.5%), t50%(3.5 min), t70%(11.6 min) while that of ratio 1:1 was the least with- m∞(48.6%), m5min(23.8%). Their release kinetics followed a KorsmeyerPeppas model with a super case-II transport mechanism.Conclusions: The drug-excipient ratios of 1:3 and 1:4 gave pharmaceutically acceptable tablets that met the British Pharmacopoeia specii cations. The t50% value of the 1:4 batch of tablets may i nd its usefulness in formulating drugs for which a fast onset of action is desired.展开更多
The main types of defect in the (Tb_(0.3)Dy_(0.7))Fe_(1.95) alloys with the 'one-step' directional solidification process were investigated. The effect of the dendrite, grain boundaries, twin boundaries, and R...The main types of defect in the (Tb_(0.3)Dy_(0.7))Fe_(1.95) alloys with the 'one-step' directional solidification process were investigated. The effect of the dendrite, grain boundaries, twin boundaries, and REFe_3 precipitates on the magnetostrictive response of the (Tb_(0.3)Dy_(0.7))Fe_(1.95) alloys was analyzed respectively. The experiment results demonstrate that the dendrite, twin boundaries, and REFe_3 precipitates can be avoided by modifying alloying ingredient, solidification parameters and annealing technique. The dendritic growth front often leads to dendrite sheet, rare earth-rich phase, and twin boundaries. The lower proportion of rare earth, or slow solidification rate, results in the occurrence of REFe_3 precipitatates. It is vital for diminishing the defects to control the undercooling of solid-liquid interface at (2.4～5.1)×10~4 K·s·cm^(-2) so that the crystal grows in cellular growth front.展开更多
The successful fabrication of layered hybrid beads by DLM process is limited by dissimilar melting ranges of different powders.For the application of DLM process into manufacturing industries,target mechanical propert...The successful fabrication of layered hybrid beads by DLM process is limited by dissimilar melting ranges of different powders.For the application of DLM process into manufacturing industries,target mechanical properties of final product must be achieved.Process analysis was performed for the DLM fabrication of layered hybrid beads by using stainless steel (SS 316L) and titanium powders.For the analysis of fabrication characteristics,single hybrid bead was formed using SS316L powder onto the base plate and then Ti powder was melted onto the previous melted layer.In addition,multi-layer hybrid beads were fabricated for the analysis of the layering effects between them.From these studies,the effects of the processing parameters,such as laser power,scan rate and scan line spacing on surface morphology were characterized and optimum processing conditions for the DLM fabrication of layered hybrid beads were developed.展开更多
Laser direct deposition （LDD） of metallic components is an advanced technology of combining CAD/CAM （computer aided design/computer aided manufacturing）, high power laser, and rapid prototyping. This technology us...Laser direct deposition （LDD） of metallic components is an advanced technology of combining CAD/CAM （computer aided design/computer aided manufacturing）, high power laser, and rapid prototyping. This technology uses laser beam to melt the powders fed coaxiaUy into the molten pool by the laser beam to fabricate fuUy dense metallic components. The present article mainly studies the LDD of Ti-6Al-4V alloy, which can be used to fabricate aircraft components. The mechanical properties of the Ti-6Al-4V alloy, fabricated by LDD, are obtained using the tension test, and the oxygen content of used powders and deposited specimens are measured. In the present article, it can be seen that the mechanical properties obtained using this method are higher than the ones obtained by casting, and equal to those got by wrought anneal. One aircraft part has been made using the LDD process. Because of this aircraft part, with sophisticated shape, the effect of the laser scanning track on the internal soundness of the deposited part was discussed.展开更多
To improve the resolution and accuracy of Direct Position Determination(DPD),this paper investigates the problem of positioning multiple emitters directly with a single moving Rotating Linear Array(RLA).Firstly,the ge...To improve the resolution and accuracy of Direct Position Determination(DPD),this paper investigates the problem of positioning multiple emitters directly with a single moving Rotating Linear Array(RLA).Firstly,the geometry of the RLA is formulated and analysed.According to its geometry,the intercepted noncoherent signals in multiple interception intervals are modeled.Correspondingly,the Multiple SIgnal Classification(MUSIC)based noncoherent DPD approach is proposed.Secondly,the synchronous coherent pulse signals are individually considered and formulated.And the coherent DPD approach which aims for localizing this special type of signal is presented by stacking all array responses at different interception intervals.Besides,we also derive the constrained Cramer-Rao Lower Bound(CRLB)expression for both noncoherent and coherent DPD with RLA under the constraint that the altitudes of the emitters are known.At last,computer simulations are included to examine the performance of the proposed approach.The results demonstrate that the localization accuracy and resolution of DPD with single moving linear array can be significantly improved by the array rotation.In addition,coherent DPD with RLA further improves the resolution and increases the maximum emitter number that can be localized compared with the noncoherent DPD with RLA.展开更多
In bistaic acoustic testing, there will be strong direct blast interference. An algorithm based on signal phase-matching array processing that rejects direct blast interference in bistatic acoustic testing has been st...In bistaic acoustic testing, there will be strong direct blast interference. An algorithm based on signal phase-matching array processing that rejects direct blast interference in bistatic acoustic testing has been studied, through which the object scattering signal is accurately extracted. Characteristics of bistatic acoustic testing and signal phase matching processing principle are fully integrated in this algorithm. Firstly, the direct blast interference is calculated from the receiving signal based on three subarrays signal phase matching processing. Secondly, the direct blast is rejected by subtraction from the receiving signal. In this way the limitations of the high signal to noise ratio that signal phase matching processing required for direct calculating the object scattering signal can be avoided. Simulation and sea trial results show that, when the ratio of signal to interference is greater than -20 dB, this algorithm of direct blast interference rejection based phase matching signal processing can accurately extract the object scattering signal.展开更多
文摘The effect of copper concentration on the performance of the catalytic reaction between silicon and methyl chloride was investigated using online gas chromatogram. The catalyst concentration greatly influences various aspects of the direct organosilane synthesis process, including the reaction rate, the selec- tivity, and the silicon conversion. The reaction activity and the silicon conversion increase as the catalyst concentration increases. However, the reaction selectivity decreases for the catalyst concentrations more .than 9 wt.%. The cross-sections of deactivated contact mass particles were observed by optical microscopy and analyzed by scanning electron microscope combined with energy dispersive X-ray detector （SEM-EDX） The observations showed that a textured substance formed on the original flat surface of the silicon particles after deactivation with copper only in a shallow surface layer of the contact mass. This indicates that the copper diffusion is the rate limiting step which causes the reaction deactivation.
基金the Fundamen-tal Research Funds for Central Universities(No.FRF-SD-12-013A)the State Key Laboratory of Advanced Metallurgy,China
文摘A one-dimensional unsteady mathematical model was established to describe direct reduction in a composite pellet made of metallurgical dust. The model considered heat transfer, mass transfer, and chemical reactions including iron oxide reductions, zinc oxide reduction and carbon gasification, and it was numerically solved by the tridiagonal matrix algorithm （TDMA）. In order to verify the model, an experiment was performed, in which the profiles of temperature and zinc removal rate were measured during the reduction process. Results calculated by the mathematical model were in fairly good agreement with experimental data. Finally, the effects of furnace temperature, pellet size, and carbon content were investigated by model calculations. It is found that the pellet temperature curve can be divided into four parts according to heating rate. Also, the zinc removal rate increases with the increase of furnace temperature and the decrease of pellet size, and carbon content in the pellet has little influence on the zinc removal rate.
基金Supported by the Natural Science Fundamental Research Project of Jiangsu Colleges and Universities under Grant No.10KJB140002
文摘With a weak hyperon-hyperon （YY） interaction deduced from the new experimental data of AA potential, this paper has performed a calculation of the direct Urca （DURCA） processes in the framework of the relativistic mean field theory （RMFT） including σ＊ and φ mesons, in comparison with the results calculated with the strong YY interaction and with no （σ＊ ,φ ） mesons included. In neutron star matter, the weak YY interaction supplies the additional repulsive interaction between hyperons while the strong YY interaction supplies the attractive one. With the weak YY interaction, the effective masses of hyperons are larger than those with the strong YY interaction while smaller than those with no （σ＊ ,φ） mesons included. The threshold star masses for the DURCA processes involving nucleons and A are not sensitive to the strength of the YY interaction. The weak YY interaction leads to larger threshold masses for the DURCA process involving [1]1 and [1]0 than the other two cases. The process involving [1]0 can take place in the neutron star only when the weak YY interaction is used. The weak YY interaction is able to bring in the agreement with the observation of the neutron star with larger mass and faster cooling than the strong YY interaction.
基金Supported by National Natural Science Foundation of China under Grant Nos. 10675024, 11075063the National Fundamental Fund project Subsidy Funds of Personnel Training J0730311
文摘In the framework of the relativistic mean field theory （RMFT）, the relativistic energy losses of the direct Urea processes with hyperons （Y-DURCA ） for reactions A → p ＋ e ＋ υe and ≡^-→ A＋e＋υe are studied in neutron stars. We calculate the energy gap of A hyperons and investigate the effects of the ^1S0 superfluidity （SF） of A hyperons on the Y-DURCA processes. The calculated results are in line with the recent experimental data △ BAA ～ 1.01 ±0.20-0.11^＋0.18 MeV. The results indicate that the ^1S0 SF of A hyperons exists in most density ranges of happening the two reactions. The theoretical cooling curves are in agreement with observation data.
文摘In non-homogeneous environment, traditional space-time adaptive processing doesn＇t effectively suppress interference and detect target, because the secondary data don＇ t exactly reflect the statistical characteristic of the range cell under test. A ravel methodology utilizing the direct data domain approach to space-time adaptive processing （ STAP ） in airbome radar non-homogeneous environments is presented. The deterministic least squares adaptive signal processing technique operates on a ＂snapshot-by-snapshot＂ basis to dethrone the adaptive adaptive weights for nulling interferences and estimating signal of interest （SOI）. Furthermore, this approach eliminates the requirement for estimating the covariance through the data of neighboring range cell, which eliminates calculating the inverse of covariance, and can be implemented to operate in real-time. Simulation results illustrate the efficiency of interference suppression in non-homogeneous environment.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11574362,61210014,and 11374340the Innovative Clean-Energy Research and Application Program of Beijing Municipal Science and Technology Commission under Grant No Z151100003515001
文摘The resonant excitation is used to generate photo-excited carriers in quantum wells to observe the process of the carriers transportation by comparing the photoluminescence results between quantum wells with and without a p-n junction. It is observed directly in experiment that most of the photo-excited carriers in quantum wells with a p-n junction escape from quantum wells and form photoeurrent rather than relax to the ground state of the quantum wells. The photo absorption coei^cient of multiple quantum wells is also enhanced by a p-n junction. The results pave a novel way for solar cells and photodetectors making use of low-dimensional structure.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11447165,11373047 and 11265009the Youth Innovation Promotion Association of Chinese Academy of Sciences under Grant No 2016056
文摘The relativistic neutrino emissivity of the nucleonic direct URCA processes in neutron star matter is investigated within the relativistic Hartree-Fock approximation. We particularly study the influences of the tensor couplings of vector mesons ω and ρ on the nucleonic direct URCA processes. It is found that the inclusion of the tensor couplings of vector mesons w and p can slightly increase the maximum mass of neutron stars. In addition, the results indicate that the tensor couplings of vector mesons ω and ρ lead to obvious enhancement of the total neutrino emissivity for the nucleonic direct URCA processes, which must accelerate the cooling rate of the non- superfluid neutron star matter. However, when considering only the tensor coupling of vector meson ρ, the neutrino emissivity for the nucleonic direct URCA processes slightly declines at low densities and significantly increases at high densities. That is, the tensor coupling of vector meson ρ leads to the slow cooling rate of a low-mass neutron star and rapid cooling rate of a massive neutron star.
基金Project(cstc 2018 jszx-cyzdx 0100)supported by the Chongqing Technology Innovation and Application Demonstration Project,China。
文摘In this study,innovative ellipsoid pellet with craters on its surface was designed,and the direct reduction process was compared with ellipsoid(without craters)and sphere pellets.In addition,furnace temperature and uneven heat flux density effects on the pellet direct reduction process were also studied.The results show that ellipsoid pellet is better than that of spherical pellet on metallization ratio.However,under the condition of non-uniform heat flow,the ellipsoid pellet final metallization rate and zinc removal rate were lower.Although the heat transfer effect of ellipsoid pellet with craters was not improved significantly,the metallization rate and zinc removal rate were found improved,which will have a cumulative effect on the pellets direct reduction process in rotary hearth furnace.Under varying furnace temperature conditions,the pellet temperature was higher than that of the constant furnace temperature.After 1200 s,pellet Fe concentration increased to 123.6%,metallization rate and zinc removal rate increased to 113.7%and 102.2%,respectively.These results can provide references for the carbon-containing pellet design used in rotary hearth furnace.
基金financially supported by the National Natural Science Foundation of China (No. 51674026)
文摘Currently, the majority of copper tailings are not effectively developed. Worldwide, large amounts of copper tailings generated from copper production are continuously dumped, posing a potential environmental threat. Herein, the recovery of iron from copper tailings via low-temperature direct reduction and magnetic separation was conducted; process optimization was carried out, and the corresponding mineralogy was investigated. The reduction time, reduction temperature, reducing agent (coal), calcium chloride additive, grinding time, and magnetic field intensity were examined for process optimization. Mineralogical analyses of the sample, reduced pellets, and magnetic concentrate under various conditions were performed by X-ray diffraction, optical microscopy, and scanning electron microscopy-energy-dispersive X-ray spectrometry to elucidate the iron reduction and growth mechanisms. The results indicated that the optimum parameters of iron recovery include a reduction temperature of 1150A degrees C, a reduction time of 120 min, a coal dosage of 25%, a calcium chloride dosage of 2.5%, a magnetic field intensity of 100 mT, and a grinding time of 1 min. Under these conditions, the iron grade in the magnetic concentrate was greater than 90%, with an iron recovery ratio greater than 95%.
基金The research is funded by the National Natural Science FOundation of China! (No.59931030)
文摘The solute redistribution in directional melting process is theoretically studied. Based on quantitative evaluations, uniform.solute distribution in liquid and a quasi-steady solute distribution in solid are supposed. The discussion on the solute balance comes to a simple model for the solute redistribution in directional melting process. As an example, the variation of liquid composition during melting process of carbon steel is quantitatively evaluated using the model. Results show that the melting of an alloy starts at solidus temperature, but approaches the liquidus temperature after a very short transient process.
文摘The microstructures and mechanical properties of a series of direct-quenched steels containing,in weight percent,from 0.05 to 0.20 carbon,0.20 to 0.40 silicon,1.10 to 1.70 manganese and at least one microalloying element of vanadium,niobium,titanium and boron have been investigated.After controlled rolling,these steels were cooled in spray water to 400,300 and 200℃,respectively and then cooled in still air.Comparison of the Charpy V-notch impact toughness of direct-quenched steels without subsequent tempering was made with that of direct-quenched steels tempered at 600℃.It is found that an attractive combination of strength and toughness is achived by means of direct-quenching.There exists two types of microstructures in accordance with carbon equivalent.Lath martensitic microstructure is obtained for C>0.4%,granular bainitic microstructures for C.< 0.35%and mixtures of martensite and bainite for C,.in the range of 0.35— 0.40%.The effect of interrupted quenching temperature on microstructure is not significant for low C.steel,but interrupted quenching temperature has a strong effect on microstructure for high C,.steel.
文摘A novel universal preprocessing method is proposed to estimate angles of arrival,which is applicable to one-or two-dimensional high resolution processing based on arbitrarycenter-symmetric arrays (such as uniform linear arrays, equal-spaced rectangular planar arraysand symmetric circular arrays). By mapping the complex signal space into the real one, the newmethod can effectively reduce the computation needed by the signal subspace direction findingtechniques without any performance degradation. In addition, the new preprocessing scheme itselfcan decorrelate the coherent signals received on the array. For regular array geometry such asuniform linear arrays and equal-spaced rectangular planar arrays, the popular spatial smoothingpreprocessing technique can be combined with the novel approach to improve the decorrelatingability. Simulation results confirm the above conclusions.
基金supported by the National Key Basic Research Program (973 program) (No. 2006CB100205)the National Science Fund for Distinguished Young Scholars (No. 30825030)+2 种基金the National Natural Science Foundation of China (No. 30770466, 90717110, 30970260 and 30971752)the Earmarked Fund for Modern Agro-industry Technology Research System (No. nycytx-01)the National High Technology Research and Development Program of China (863 Program) (No. 2007AA10Z100)
文摘In several stress responsive gene loci of monocot cereal crops,we have previously identified an unusual posttranscriptional processing mediated by paired presence of short direct repeated （SDR） sequences at 5＇ and 3＇ splicing junctions that are distinct from conventional （U2/U12-type） splicing boundaries.By using the known SDR-containing sequences as probes,24 plant candidate genes involved in diverse functional pathways from both monocots and dicots that potentially possess SDR-mediated posttranscriptional processing were predicted in the GenBank database.The SDRs-mediated posttranscriptional processing events including cis-and trans-actions were experimentally detected in majority of the predicted candidates.Extensive sequence analysis demonstrates several types of SDR-associated splicing peculiarities including partial exon deletion,exon fragment repetition,exon fragment scrambling and trans-splicing that result in either loss of partial exon or unusual exonic sequence rearrangements within or between RNA molecules.In addition,we show that the paired presence of SDR is necessary but not sufficient in SDR-mediated splicing in transient expression and stable transformation systems.We also show prokaryote is incapable of SDR-mediated premRNA splicing.
文摘Objective: To characterise a novel multifunctional pharmaceutical excipient and investigate its ef ect on paracetamol release from tablets prepared by direct compression.Methods: The excipient was prepared by co-processing gelatinized maize starch with sodium carboxymethyl cellulose and microcrystalline cellulose in a ratio of 2:1:1, dried and pulverized into powder. The excipient formulated was characterized using Fourier transform infrared spectroscopy and dif erential scanning calorimetry. The excipient was used to prepare batches of tablets by direct compression with drug-excipient ratios of 1:1, 1:2, 1:3 and 1:4. Parameters evaluated on tablets include crushing strength, friability and in vitro dissolution studies. Results: Differential scanning calorimetry analysis revealed a crystalline excipient while Fourier transform infrared spectroscopy showed no interaction between the excipient and paracetamol. Tablets from all the batches gave average crushing strength values between 3.47 and 4.88 kp. The 1:1 and 1:2 tablet batches were comparable to each other while 1:3 and 1:4 were also comparable to one another in their dissolution proi les. The dissolution parameters of the 1:4 batch was faster with- m∞(90.5%), t50%(3.5 min), t70%(11.6 min) while that of ratio 1:1 was the least with- m∞(48.6%), m5min(23.8%). Their release kinetics followed a KorsmeyerPeppas model with a super case-II transport mechanism.Conclusions: The drug-excipient ratios of 1:3 and 1:4 gave pharmaceutically acceptable tablets that met the British Pharmacopoeia specii cations. The t50% value of the 1:4 batch of tablets may i nd its usefulness in formulating drugs for which a fast onset of action is desired.
文摘The main types of defect in the (Tb_(0.3)Dy_(0.7))Fe_(1.95) alloys with the 'one-step' directional solidification process were investigated. The effect of the dendrite, grain boundaries, twin boundaries, and REFe_3 precipitates on the magnetostrictive response of the (Tb_(0.3)Dy_(0.7))Fe_(1.95) alloys was analyzed respectively. The experiment results demonstrate that the dendrite, twin boundaries, and REFe_3 precipitates can be avoided by modifying alloying ingredient, solidification parameters and annealing technique. The dendritic growth front often leads to dendrite sheet, rare earth-rich phase, and twin boundaries. The lower proportion of rare earth, or slow solidification rate, results in the occurrence of REFe_3 precipitatates. It is vital for diminishing the defects to control the undercooling of solid-liquid interface at (2.4～5.1)×10~4 K·s·cm^(-2) so that the crystal grows in cellular growth front.
基金Project(2012-0000-965)supported by the National Core Research Center Program through the National Research Foundation of Korea Funded by the Ministry of Education,Science and Technology
文摘The successful fabrication of layered hybrid beads by DLM process is limited by dissimilar melting ranges of different powders.For the application of DLM process into manufacturing industries,target mechanical properties of final product must be achieved.Process analysis was performed for the DLM fabrication of layered hybrid beads by using stainless steel (SS 316L) and titanium powders.For the analysis of fabrication characteristics,single hybrid bead was formed using SS316L powder onto the base plate and then Ti powder was melted onto the previous melted layer.In addition,multi-layer hybrid beads were fabricated for the analysis of the layering effects between them.From these studies,the effects of the processing parameters,such as laser power,scan rate and scan line spacing on surface morphology were characterized and optimum processing conditions for the DLM fabrication of layered hybrid beads were developed.
基金This work was supported by the National Natural Science Foundation of China （No. 50331010）
文摘Laser direct deposition （LDD） of metallic components is an advanced technology of combining CAD/CAM （computer aided design/computer aided manufacturing）, high power laser, and rapid prototyping. This technology uses laser beam to melt the powders fed coaxiaUy into the molten pool by the laser beam to fabricate fuUy dense metallic components. The present article mainly studies the LDD of Ti-6Al-4V alloy, which can be used to fabricate aircraft components. The mechanical properties of the Ti-6Al-4V alloy, fabricated by LDD, are obtained using the tension test, and the oxygen content of used powders and deposited specimens are measured. In the present article, it can be seen that the mechanical properties obtained using this method are higher than the ones obtained by casting, and equal to those got by wrought anneal. One aircraft part has been made using the LDD process. Because of this aircraft part, with sophisticated shape, the effect of the laser scanning track on the internal soundness of the deposited part was discussed.
基金funded by the National Defence Science and Technology Project Fund of China(No.3101140)the Shanghai Aerospace Science and Technology Innovation Fund of China(No.SAST2015028)the Equipment Prophecy Fund of China(No.9140A21040115KG01001).
文摘To improve the resolution and accuracy of Direct Position Determination(DPD),this paper investigates the problem of positioning multiple emitters directly with a single moving Rotating Linear Array(RLA).Firstly,the geometry of the RLA is formulated and analysed.According to its geometry,the intercepted noncoherent signals in multiple interception intervals are modeled.Correspondingly,the Multiple SIgnal Classification(MUSIC)based noncoherent DPD approach is proposed.Secondly,the synchronous coherent pulse signals are individually considered and formulated.And the coherent DPD approach which aims for localizing this special type of signal is presented by stacking all array responses at different interception intervals.Besides,we also derive the constrained Cramer-Rao Lower Bound(CRLB)expression for both noncoherent and coherent DPD with RLA under the constraint that the altitudes of the emitters are known.At last,computer simulations are included to examine the performance of the proposed approach.The results demonstrate that the localization accuracy and resolution of DPD with single moving linear array can be significantly improved by the array rotation.In addition,coherent DPD with RLA further improves the resolution and increases the maximum emitter number that can be localized compared with the noncoherent DPD with RLA.
基金supported by the Foundation of Key Laboratory for Underwater Test & Control Technology under Grant No.9140C260201110C26
文摘In bistaic acoustic testing, there will be strong direct blast interference. An algorithm based on signal phase-matching array processing that rejects direct blast interference in bistatic acoustic testing has been studied, through which the object scattering signal is accurately extracted. Characteristics of bistatic acoustic testing and signal phase matching processing principle are fully integrated in this algorithm. Firstly, the direct blast interference is calculated from the receiving signal based on three subarrays signal phase matching processing. Secondly, the direct blast is rejected by subtraction from the receiving signal. In this way the limitations of the high signal to noise ratio that signal phase matching processing required for direct calculating the object scattering signal can be avoided. Simulation and sea trial results show that, when the ratio of signal to interference is greater than -20 dB, this algorithm of direct blast interference rejection based phase matching signal processing can accurately extract the object scattering signal.
